1. Field of the Invention
The present invention relates to a method for managing a key of a home device. More particularly, the present invention relates to a method and a system for managing a key of a home device in a broadcast encryption (BE) system
2. Description of the Related Art
BE is a method of effectively transmitting information only to a desired set of users of the total number of users capable of receiving information from a transmitter, which is, for example, a broadcast center. Thus, the BE must be effectively used in a case of an arbitrary and dynamic variation in a set of users who is to receive information. An important property of the BE is to revoke or exclude an undesired device or user, for example, an illegal user or an expired user.
For this purpose, each device is allotted and stores a set of different keys, and a service provider stores a set of all keys of all devices. If a device to be excluded is determined, the service provider encrypts a temporal key using other keys except a key of the corresponding device, encrypts data to be transmitted using the temporal key, and broadcasts the encrypted temporal key and the encrypted data.
The device analyzes received data, selects a key to be used for decryption from the stored set of keys, decrypts the encrypted temporal key, and decrypts the encrypted data. A BE system adopts various techniques that have been suggested but generally adopts a hierarchical node structure.
In the BE, a transmission overhead, a storage overhead, and a computation overhead are important. The transmission overhead, the storage overhead, and the computation overhead respectively mean an amount of a header to be transmitted from a transmitter, an amount of secret keys to be stored by a user, and an amount of computation the user requires to obtain a session key. It is very important to reduce the transmission overhead.
In a BE system having a hierarchical structure according to the prior art, not the lower nodes of a home server to which a corresponding device belongs, but the leaf nodes that are lowermost nodes are randomly or in manufacturing order allocated to a specific device
In other words, in a case where a service provider provides services only to devices controlled by a specific home server, devices except devices belonging to the home sever must be regarded as revoked devices.
According to the BE system having the hierarchical structure according to the prior art, in the worst case, for example, in a case where devices are uniformly distributed in each home server, data must be transmitted to devices using different keys. Thus, the transmission overhead of the BE system cannot be reduced.